In wireless systems, a front-end module (FEM) provides an interface between an antenna and a radio frequency (RF) transceiver. A FEM typically includes power amplifiers, switches, low-noise amplifiers, control circuitry, and passive elements. Complex wireless systems, exemplified by smart phones, utilize large numbers of switches (e.g. antenna switch connecting to multiple RF chains, band selection, incorporating diversity antennae, etc.). A conventional switch needs a continuously on supply voltage and control bits to operate the switch devices. The continuously on supply voltage is used to generate internal voltages (Von and Voff), which operate the switch device with good performance. The digital control bits control the switch device by determining which of the internal voltages are routed to individual RF field effect transistor (FET) gates using respective input buffers. The continuously on supply voltage and internal voltage generator are an additional drain on a battery of the smart phone.
It would be desirable to implement an RF switch with a digital gate threshold voltage.